1. Field of the Invention
The present invention relates to a servo motor drive control device having a function of calculating consumed electric energy and regenerated electric energy of a mechanical system or especially a machine tool having a plurality of servo motors.
2. Description of the Related Art
Generally, as disclosed, for example, in Japanese Unexamined Utility Model Publication No. 4-25485, consumed electric energy of a mechanical system can be determined by connecting a wattmeter to an original power source. Further, in a mechanical system having a plurality of servo motors, it is known that consumed electric energy for each servo motor is determined in more detail, and regenerated electric energy, which may be generated in the servo motors, is also determined.
As such a technique, Japanese Unexamined Patent Publication No. 2000-105605 discloses that consumed electric power and regenerated electric power of each servo motor are determined for each predetermined period from an angular velocity of each servo motor and a measurement value of an electric current flowing through the servo motor and then consumed electric energy and regenerated electric energy are determined by integrating the determined consumed electric power and determined regenerated electric power over a predetermined length of time. Japanese Unexamined Patent Publication No. 2000-105605 states that a proper maintenance/inspection time can be grasped by using the thus determined consumed electric energy and regenerated electric energy to evaluate operating loads for individual axes corresponding to individual servo motors. It is also proposed to try to optimize processes and magnitudes of regeneration resistances corresponding to individual servo motors so as to assure a balance of loads between the axes.
Japanese Unexamined Patent Publication No. 2000-206150 discloses that consumed electric energy per product manufacture cycle is determined for each power consuming element such as a servo motor or a heater of an injection molding machine. This reference states that it makes it possible to accurately determine the product manufacturing cost or to evaluate an effect that the operation condition of the machine has on the consumed electric energy to thereby try to effectively utilize the electric power.
Japanese Unexamined Patent Publication No. 2005-313610 discloses that consumed electric power of motors of a paper feed mechanism and carriage drive mechanism is monitored in a printer to suppress an adverse effect due to heat of the motors.
Please note that in Japanese Unexamined Patent Publication No. 2000-206150 and Japanese Unexamined Patent Publication No. 2005-313610, the consumed electric power of the servo motor is determined from the measurement value of the electric current of the servo motor.
In a mechanical system having a lot of servo motors, a power source configuration may be employed in which the servo motors are divided into a plurality of groups and a plurality of the servo motors associated with each group are connected to a common power source unit. Specifically, this power source configuration includes a plurality of amplifier groups, each of which is configured by one common power source unit, and a plurality of power supply units connected to the common power source unit each for supplying power to each of the plurality of the servo motors, and all of the amplifier groups are connected to a higher-level power source system such as an AC power source network.
In this power source configuration having a plurality of amplifier groups, the evaluation of the consumed electric energy and regenerated electric energy according to the prior art described above is sometimes insufficient. For example, it is impossible to know whether the regenerated electric energy of each servo motor is returned to the AC power source or effectively used by other servo motors. Each of amplifier groups also can employ a different regeneration method, i.e., a resistance regeneration method or a power regeneration, and the regenerated electric energy is sometimes disposed of by the regeneration resistance. As described above, the prior art does not focus attention on clarification of a flow of the regenerated electric energy.